Continuous carbon fiber tapes

ABSTRACT

Tape containing continuous high strength high modulus carbon fibers and optionally also glass fibers suitable for use as preimpregnated tape in mechanical winding processes is disclosed wherein there is a light cross-weave of 1-10 filaments of fine glass fiber at a frequency of about 10-2 threads per inch.

United States Patent I 117/161 LC, 228; 57/140 G; 161/87, 88, 90, 91,92, 93; 139/383 R, 384 R, 420 R, 420 G; 28/75 Phillips 1 June 13, 1972[54] CONTINUOUS CARBON FIBER TAPES [56] References Cited [72] inventor:Leslie Nathan Phillips, Famborough, En- UNITED STATES PATEMS l d 92,962,386 11/1960 Doll et a1. ..1 17/228 [73] Assignee: Minister ofTechnology in Her Brltannic 3,073,004 1/1963 l i l39/420 MajestysGovernment of the United Klng- 3,239,403 3/ 1966 Williams.. 17/228 domor Great Britain and Northern Ire- 3,444,l20 5/1969 Boyes 117/161 28land, London, England 3,494,888 2/1970 McEh-oy ..i 17/ 161 28 1 Filed:March 6, 1970 FOREIGN PATENTS 0R APPLICATIONS [21] Appi- No.1 17,265790,216 2/1958 Great Britain ..l39/420 G Primary Examiner-Henry S.Jaudon [30] Foreign Appncmon Priority V Attorney-Stevens, Davis, Miller& Mosher March 10, 1969 Great Britain.... I 2 Nov. 6, 1969 Great Britain..54,452/69 [57] ABSTRACT I Tape containing continuous high strengthhigh modulus car- [52] 11.8. CI. ..l39/420 R, wit/28088621493, honfibers and optionally also glass fibers suitablefor use as 139/pre-impregnated tape in mechanical winding processes is dis- [51] Illl.Cl. "D0311 15/00 closed wherein there is a light crmweave f 0 filaments[58] FieldoiSeerch ..117/161ZB,161P,161LE,

of fine glass fiber at a frequency of about 10-2 threads per inch.

10 Claims, 1 Drawing Figure CONTINUOUS CARBON FIBER TAPES The presentinvention relates to tape containing unidirectional carbon fibers whichmay be resin impregnated and used to produced reinforced plasticarticles by applying to or winding on a former followed by curing.

It is well known to produce composite shaped articles by winding a resinpre-impregnated tape upon a former or mandrel of a suitable shape andthen to place the former and tape in a mould either without furtheraddition of resin or after further resin has been impregnated into thetape. However, it has been discovered that the parallel alignment of thereinforcing fibers in the tape is not retained in the mould because inthe early stages of cure the resin is liquid and under the influence ofthe hydrostatic pressure in the liquid resin the individual reinforcingfibers in the pre-impregnated tape are forced apart and the phenomenonknown as barrelling takes place. This results in misalignment of thereinforcing fibers and may lead to failure to realize the full strengthpossible of the composite material.

Misalignment of fibers in carbon fiber reinforced articles can causeweakness because the relatively small extension at break of carbonfibers means that in a composite in which the fibers are not properlyaligned individual fibers may fail before other fibers in a differentorientation are taking an appreciable proportion of the load.

In accordance with the present invention, a tape containingunidirectional carbon fiber comprises a plurality of warp members, whichinclude carbon fiber tows, and a continuous weft-thread woven throughsaid warp members at a frequency of between about and 2 threads per inchsaid weft thread being arranged to maintain the warp members parallel toand contiguous with one another.

Normally the warp members are not individual filaments but aggregationsof individual filaments and conveniently a warp member is a tow ofcarbon fiber of about 10,000 ends or filaments although for particularpurposes the number of ends or filaments in any given carbon fiber towwarp member may be any number down to about 500 as may be convenient.

The warp members may be entirely carbon tows or a proportion thereof maybe replaced by bundles or tows of glass fiber and up to 90 percent byweight of the total warp may be bundles or tows of glass fiber.

Tows of carbon fiber and tows of glass fiber may alternate as warpmembers or a plurality of adjacent warp membersmay be of carbon fibersand/or a plurality of adjacent warp members may be of glass fiber sothat the tape has a banded structure wherein the carbon and glass fiberare grouped together in the warp. In an extreme example a single tow ofglass fiber or a single tow of carbon fibers may be interposed betweentwo groups of fiber of the opposite type. For example if a tapecontaining both carbon fiber and glass fiber has to be trimmed at theedges it is more economical to have the edges to be trimmed off entirelyof glass fiber because of the cost of car bon fiber, so long as thisdoes not detract from the properties of the finished composite.

Conveniently the tows of glass fiber and tows of carbon fiber aresubstantially the same size so that the weave of the finally producedtape remains even. The sizes may, however, vary quite markedly if thisdoes not spoil the evenness of the weave of the finally produced tape orpermit misalignment of the carbon fibers in a finally produced compositesuch that an appreciable number of carbon fibers break under strainbefore substantially all the carbon fibers are loaded.

Preferably the unidirectional carbon fiber tows of the warp members areof high strength high modulus carbon fiber manufactured by one or moreof the processes described in the specifications of [1.11. Pat. Nos.1,110,791, 1,148,874, 1,166,251, 1,166,252, 1,168,619, 1,180,441 andU.K. application No. 28881/66 now UK. Pat. No. 1,193,263.

The carbon fiber tows of this invention include high strength highmodulus carbon fiber produced by one or more of the processes describedin U.S. Pat. No. 3,412,062.

In U.S. Pat. No. 3,412,062, there is described a method of making carbonfibers having a Young's modulus parallel to the fiber axis of not lessthan 16 X 10 pounds per square inch comprising the steps of oxidizing anorganic polymer fiber by simultaneously heating the fiber in anoxidizing atmosphere at a temperature of from about 200 to 250C for atime suffcient to permit substantially complete permeation of oxygenthroughout the core of the fiber while the fiber is held underlongitudinal tension, said tension being sufficient at least to limitshrinkage of the fibers during heating to not more than about 12 percentof the length of the fiber, and carbonizing the fiber by heating theoxidized fiber in a non-oxidizing atmosphere to a temperature of up toabout at least 1,000C. Preferably the organic polymer fiber ispolyacrylonitrile.

It is to be noted that the term polyacrylonitrile fibers is used bythose skilled in this art to include copolymers or terpolymers ofacrylonitrile with other monomers e.g. methyl methacrylate or vinylacetate, either alone or to which have been added polymers compatiblewith them for example phenolic resins or Friedel-Crafts condensates. ltis in this sense that the term polyacrylonitrile fibers is usedthroughout said U.S. Pat. No. 3,412,062.

The high temperature carbonizing is performed under vacuum or in anonoxidizing atmosphere such as hydrogen.

The preliminary low temperature oxidizing step which forms part of saidmethod should not be of too short duration as the fibers are then leftwith a soft core and upon subsequent high temperature heat treatmentholes are formed in the resulting fibers.

In a further embodiment according to said U.S. Pat. No. 3,412,062, aprocess of producing carbon fibers comprises initially heating fibers ofpolyacrylonitrile while held under tension in an oxidizing atmosphere atfrom 200-250C for suffcient time to permit substantially completepermeation of oxygen throughout the individual fibers and subsequentfurther heating of the fibers so formed to a carbonizing temperature ofat least 1,000C under non-oxidizing conditions.

The duration of the initial heating required will depend to a largeextent on the diameter of the fibers concerned but for a temperature of220C complete oxygen permeation of the fibers takes place after heatingfor about 24 hours for 2% denier fibers and after about 50 hours for 4%denier fibers.

The fibers are tensioned so that longitudinal shrinkage which normallytakes place during this initial heating is reduced, eliminated or issuch as to cause the fibers to elongate.

Further improvements in the characteristics of the fibers produced areachieved if, subsequent to carbonizing to about 1,000C the fibers arefurther heat treated to above 2,000C in a non-oxidizing atmosphere.

The tensioning of fibers may also be maintained during the subsequentcarbonizing and/or heat treatment.

For further details, please refer to the: examples of said U.S. Pat. No.3,412,062.

The weft is intended to prevent the phenomenon of barrelling describedabove and maintain the fibers in alignment and the material used isselected to be sufficiently strong to achieve this end although it mustalso be selected to be compatible with the unidirectional carbon fiberused as reinforcement, with the plastic to be reinforced, and with anyadditive thereto.

The weft thread may be of continuous carbon fiber but this is not ingeneral successful. Advantageously the weft thread is glass fiber and ithas been found that between 1 and 10 ends or filaments of fine glassfiber is preferred.

An embodiment of the invention is illustrated in the accompanyingdrawing in which A represents warp members which may be tows of carbonfiber or a mixture of tows of carbon fiber and tows of glass fiber asdescribed above and B represents the continuous weft thread, which iswoven at a frequency of between about 10 and 2 threads per inch andwhich is between 1 and 10 filaments of :fine glass fiber. Moreparticularly, as shown in said drawing, B represents the continuous weftthread, which is continuously woven throughout the length of said warpmembers and zigzaggedly crossing said warp members at an oblique angleat a frequency of between about 10 and 2 threads per inch.

The tape may be woven by the well known means of the weaving art andpreferably prior to the weaving process the carbon fiber tows aretreated by the process of dressing described in U.l(. Pat. ApplicationNos. 52,653/67 and 4,711/68, now issued as a single U.K. Pat. No.1,195,219 which discloses a dressing for facilitating the handling andprocessing of carbon fibers comprising a dilute solution of not morethan 35 percent by weight of resin in a volatile organic non-aqueoussolvent.

The resin may comprise an epoxy, phenolic, Friedel-Crafts, polyimide orpolyester resin.

Suitable solvents are acetone, ethyl acetate, methyl ethyl ketone andchlorinated hydrocarbons such as ethylene dichloride and 1.2dichloroethane.

In one example it was found that a solution of l-5 percent by weight ofepoxy resin in acetone formed a satisfactory dressing.

Examples of epoxy resins which have been used are Araldite (RegisteredTrade Mark) LY 5 58 and Shell (Registered Trade Mark) Epikote 828. Otherepoxy resins may be used, it being desirable that they should have ahigh viscosity and that brittle resins be avoided. Low viscosity resinsof the cycloaliphatic type, such as a cyclopentadiene based resin, maybe blended with other more viscous resins in order to obtain the overallrequired viscosity.

It a further example it was found that a solution of 5-20 percent byweight of polyester resin in methyl ethyl ketone formed a satisfactorydressing.

It was also found that either a hot or cold setting polyester resin wassatisfactory, e.g. Bakelite (Registered Trade Mark) S.R. 17449 resin anunsaturated polyester made from a glycol, a dicarboxylic acid and maleicanhydride has been found satisfactory.

Also, according to the present invention a process for rendering carbonfibers readily handleable comprises impregnating the fibers with adressing comprising a weak solution of resin, such as an epoxy,phenolic, Friedel-Crafts, polyimide or polyester resin in a volatileorganic non-aqueous solvent, and allowing the solvent to evaporate,evaporation of the solvent leaving the carbon fibers in a close knithandleable form.

It is to be noted that the term Friedel-Crafts resin means a resinformed from an aromatic compound with an aromatic linking agent whichhas two chloromethyl or methoxymethyl groups attached to an aromaticnucleus by means of a polycondensation reaction involving the nuclearhydrogen atoms and may be aided by the presence of a small amount of Friedel-Craft type catalyst such as stannic chloride.

Once the tape is obtained it may then be impregnated with an appropriateresin and converted to a pre-impregnated tape suitable for use asdescribed above.

Such a process lends itself to the continuous production of thin carbonfiber reinforced composite material. In an example of such a process acontinuous supply of carbon fibers, as from a process in which carbonfibers are produced continuously, are drawn in turn through a bathcontaining said dressing, a drying region in which surplus dressingdrains from the fiber and that remaining on the fibers is dried, asecond bath containing a heat catalyzed polyester resin in which thefibers are immersed and between a pair of rollers between which thecomposite material comprising the fibers, dressing which has beensoftened by the polyester resin and the resin are flattened to a tapelike form. The resin content of the tape may subsequently be cured bythe application of heat.

In one example a non-continuous process for producing a plasticscomposite material 80 grams of 10,00 filament tow carbon fibers of 7microns diameter of the type disclosed in British Pat. No. 1,110,791 andhaving an ultimate tensile strength of 280 X 10 lg/sq in. and a Youngsmodulus of 55 X 10 lb/sq in. were supported in a glass fiber clothcradle or sling and dipped into a tank containing 3 liters of polyesterresin solution comprising 1 part by weight of Bakelite (Registered TradeMark) S.R. 17,449 polyester resin and 4 parts by weight of methyl ethylketone.

After immersion for 30 seconds, the cradle supporting the fibers wasremoved from the solution and the surplus solution allowed to drain off.The fibers, with residual dressing adhering to them, were then suspendedvertically for 2 hours at room temperature until dry. The resultingclumped fibers were then incorporated as a reinforcement in a matrixcomprising parts by weight S.R. 17,449 polyester resin, 2 parts peroxidecatalyst and 2 parts cobalt naphthenate, the fibers comprisingapproximately 40 percent by volume of the resulting composite formedwhen curing of the resin was complete.

The tape of the present invention may be used advantageously when it isdesired to tension the unidirection carbon fibers while the mouldingprocess is being carried out. This has the advantage that individualcarbon fibers are aligned substantially parallel during the curingprocess and also helps to ensure that the load of the composite finallyproduced is evenly distributed among the carbon fibers. This isimportant in view of the relatively small extension at break of carbonfibers which means that in a composite in which fibers are not properlyaligned individual fibers may fail before other fibers in a differentfibers in a different orientation are taking an appreciable share of theload.

I claim:

1. A pre-impregnation tape comprising a plurality of warp membersparallel to and contiguous with one another selected from the groupconsisting of tow of glass fiber and tow of unidirectional carbonfibers, at least 10 percent by weight of said warp members consisting ofsaid tow of carbon fibers, and a continuous weft thread continuouslywoven through said warp members at a frequency of between about 10 and 2threads per inch, said weft thread being selected from the groupconsisting of continuous glass fiber and continuous carbon fiber.

2. A tape as claimed in claim 1 wherein the warp members are composedentirely of carbon fiber tow.

3. A tape as claimed in claim 1 wherein the carbon fiber tow includehigh modulus carbon fiber having a Youngs modulus parallel to the fiberaxis of not less than 16 X 10' pounds per square inch.

4. A tape as claimed in claim 1 wherein the weft thread comprisesbetween 1 and 10 filaments of glass fiber.

5. A tape as claimed in claim 1 wherein the carbon fiber tows have asurface dressing comprising a resin selected from the group consistingof epoxy, phenolic, Friedel-Crafts, polyimide and polyester resin.

6. A tape as claimed in claim 1 and impregnated with resin.

7. A pre-impregnation tape comprising a plurality of war membersparallel to and contiguous with one another selected from the groupconsisting of tow of glass fiber and tow of unidirectional carbonfibers, at least 10 percent by weight of said warp members consisting ofsaid tow of carbon fibers, and a continuous weft thread continuouslywoven throughout the length of said warp members and zigzaggedlycrossing said warp members at an oblique angle at a frequency of betweenabout 10 and 2 threads per inch, said weft thread being selected fromthe group consisting of continuous glass fiber and continuous carbonfiber.

8. A method of preparing a cured tape comprising immersing carbon fiberin a dressing solution of not more than 35 percent by weight of resin ina volatile organic non-aqueous solvent and drying to remove said solventin order to provide a dressing on said carbon fiber, preparing aplurality of warp members from tow of glass fiber and tow ofunidirectional carbon fiber comprising said dressed carbon fiber, atleast 10 percent by weight of said warp members consisting of tow ofcarbon fibers, and weaving a continuous weft thread through said warpmembers and continuously throughout the length thereof at a frequency ofbetween about methyl ethyl ethylene dichloride dichloroethane.

10. A method as claimed in claim 8 wherein the dressing solutioncomprises a 1-5 percent by weight of epoxy resin in acetone.

ketone, and 1,2-

l l i l

2. A tape as claimed in claim 1 wherein the warp members are composedentirely of carbon fiber tow.
 3. A tape as claimed in claim 1 whereinthe carbon fiber tow include high modulus carbon fiber having a Young''smodulus parallel to the fiber axis of not less than 16 X 106 pounds persquare inch.
 4. A tape as claimed in claim 1 wherein the weft threadcomprises between 1 and 10 filaments of glass fiber.
 5. A tape asclaimed in claim 1 wherein the carbon fiber tows have a surface dressingcomprising a resin selected from the group consisting of epoxy,phenolic, Friedel-Crafts, polyimide and polyester resin.
 6. A tape asclaimed in claim 1 and impregnated with resin.
 7. A pre-impregnationtape comprising a plurality of warp members parallel to and contiguouswith one another selected from the group consisting of tow of glassfiber and tow of unidirectional carbon fibers, at least 10 percent byweight of said warp members consisting of said tow of carbon fibers, anda continuous weft thread continuously woven throughout the length ofsaid warp members and zigzaggedly crossing said warp members at anoblique angle at a frequency of between about 10 and 2 threads per inch,said weft thread being selected from the group consisting of continuousglass fiber and continuous carbon fiber.
 8. A method of preparing acured tape comprising immersing carbon fiber in a dressing solution ofnot more than 35 percent by weight of resin in a volatile organicnon-aqueous solvent and drying to remove said solvent in order toprovide a dressing on said carbon fiber, preparing a plurality of warpmembers from tow of glass fiber and tow of unidirectional carbon fibercomprising said dressed carbon fiber, at least 10 percent by weight ofsaid warp members consisting of tow of carbon fibers, and weaving acontinuous weft thread through said warp members and continuouslythroughout the length thereof at a frequency of between about 10 andabout 2 threads per inch whereby said warp members are maintainedparallel to and contiguous with one another during curing of said tape,said weft thread being selected from the group consisting of continuousglass fiber and continuous carbon fiber, and curing said tape.
 9. Amethod as claimed in claim 8 wherein the solvent is selected from thegroup consisting of acetone, ethyl acetate, methyl ethyl ketone,ethylene dichloride and 1,2-dichloroethane.
 10. A method as claimed inclaim 8 wherein the dressing solution comprises a 1-5 percent by weightof epoxy resin in acetone.